It is often helpful in the glass industry, as well as other transparent medium industries, to detect the presence and surface location of conductive coatings that are applied to the surface of the non-conductive medium. Some of these coatings are classified as low emissivity (low E) coatings. These coatings are typically not visible and therefore difficult to detect without electronic assistance.
In measuring the thickness of transparent mediums such as glass and acrylic plus many others, instruments often utilize a charge coupled device (CCD array) linear image array.
One system is disclosed in the Imbrock et al. U.S. Pat. No. 8,723,944 B1, issued May 13, 2014, which was invented by several of the co-inventors herein. In the Imbrock et al. '944 system, the CCD arrays are positioned in a linear plane with an energy source, such as a laser. The instrument is positioned flat against the glass surface so that the energy of the source exits the aperture of the instrument, striking the mediums front and back surface and reflecting back onto the CCD array. In the Imbrock et al. '944 patent, the CCD array inside the enclosure of the device positioned in parallel to the substrate surface being tested. This results in a laser/energy reflection that is striking the sensor at an angle. One difficulty that occurs when the reflecting energy approaches the CCD array at an angle, is that the reflected energy will reflect inside the bandpass filter, as well as within the protective glass surface of the CCD array itself. These extra internal reflections, are in addition to the internal reflections that naturally occur within the substrate material being tested (See PRIOR ART FIG. 1). Now instead of having a set of four (4) clean reflections from the substrate surface, the sensor will measure numerous internal reflections that are created by a reflective coating, both in the substrate surface, as well as within the bandpass filter and protective glass of the CCD array, compounded by the extra internal reflections inside the substrate.
The more reflective the coating that is on the substrate, the stronger the internal reflections that will appear on the sensors measured values. When these internal reflections begin to have a measured valued that is in any way comparable to the desired (legitimate) substrate surface reflections, it is not possible to differentiate a valid surface reflection from an internal surface reflection.
Therefore, there is a continuing need for an improved, reliable and efficient method and device to detect the presence, location and type of coating applied to various media.